Problem: Solve for $r$ : $-23 + r = -4$
Answer: Add $23$ to both sides: $ \begin{eqnarray} \\ -23 + r &=& -4 \\ \\ {+23} && {+23} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{-23 + r} &\hphantom{=}& \hphantom{-4} \\ r &=& -4 {+ 23} \\ \end{eqnarray} $ Simplify. $ r = 19$